Chronic stimulation by infectious or self-antigens initiates subsets of monoclonal gammopathies of undetermined significance (MGUS), smoldering multiple myeloma (SMM), or multiple myeloma (MM). Recently, glucosylsphingosine (GlcSph) was reported to be the target of one third of monoclonal immunoglobulins (Igs). In this study of 233 patients (137 MGUS, 6 SMM, 90 MM), we analyzed the GlcSph-reactivity of monoclonal Igs and non-clonal Igs. The presence of GlcSph-reactive Igs in serum was unexpectedly frequent, detected for 103/233 (44.2%) patients. However, GlcSph was targeted by the patient’s monoclonal Ig for only 37 patients (15.9%); for other patients (44 MGUS, 22 MM), the GlcSph-reactive Igs were non-clonal. Then, the characteristics of patients were examined: compared to MM with an Epstein-Barr virus EBNA-1-reactive monoclonal Ig, MM patients with a GlcSph-reactive monoclonal Ig had a mild presentation. The inflammation profiles of patients were similar except for moderately elevated levels of 4 cytokines for patients with GlcSph-reactive Igs. In summary, our study highlights the importance of analyzing clonal Igs separately from non-clonal Igs and shows that, if autoimmune responses to GlcSph are frequent in MGUS/SMM and MM, GlcSph presumably represents the initial pathogenic event for ~16% cases. Importantly, GlcSph-initiated MM appears to be a mild form of MM disease.

NUT carcinoma is a rare malignant neoplasm characterised by recurrent NUTM1 rearrangements, initially reported in the midline. Recently, 10 cases of cutaneous NUT carcinoma with adnexal differentiation harbouring BRD3::NUTM1, NSD3::NUTM1, BRD4::NUTM1 or BRD3::NUTM2B fusions have been reported. Accordingly, ‘NUT adnexal carcinoma’ (NAC) has been introduced as a provisional tumour entity to the fifth edition of the WHO Classification of Skin Tumours.Aims: We report the histopathological, molecular genetic and epigenetic features of seven additional cases of NAC.Methods and results: The cohort consisted of four female and three male patients with a median age of 58 years. Follow‐up was available for six cases, and documented diffuse metastatic spreading leading to death at 18 months after diagnosis for one case. Histopathological examination in all cases revealed dermal/subcutaneous neoplasms composed of poorly differentiated cells with large irregular vesicular nuclei and at least focally prominent nucleoli. All cases showed areas of duct/gland formation. Using immunohistochemistry, all tumours showed diffuse NUT expression with co‐expression of SOX10 in five cases. P63 and P40 were diffusely positive in one case and confined to the periphery of the tumour nests in five cases. Molecular analysis showed BRD4::NUTM1 fusions (n = 3), BRD3::NUTM1 fusions (n = 3) and NSD3::NUTM1 (n = 1). Although being close to this latter group, methylation and transcriptional analysis revealed that NAC formed a unique cluster distinct from extracutaneous NUT carcinoma and NUTM1‐rearranged porocarcinoma.Conclusions: Our results further support the existence of primary cutaneous NAC and suggest that it may represent an entity distinct from extracutaneous NUT carcinoma.

Chronic stimulation by infectious pathogens or self-antigen glucosylsphingosine (GlcSph) can lead to monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM). Novel assays such as the multiplex infectious antigen microarray (MIAA) and GlcSph assays, permit identification of targets for >60% purified monoclonal immunoglobulins (Igs). Searching for additional targets, we selected 28 purified monoclonal Igs whose antigen was not represented on the MIAA and GlcSph assays; their specificity of recognition was then analyzed using microarrays consisting of 3760 B-cell epitopes from 196 pathogens. The peptide sequences PALTAVETG and PALTAAETG of the VP1 coat proteins of human poliovirus 1/3 and coxsackievirus B1/B3, respectively, were specifically recognized by 6/28 monoclonal Igs. Re-analysis of patient cohorts showed that purified monoclonal Igs from 10/155 MGUS/SM (6.5%) and 3/147 MM (2.0%) bound to the PALTAVETG or PALTAAETG epitopes. Altogether, PALTAV/AETG-initiated MGUS are not rare and few seem to evolve toward myeloma.